This invention relates to a liquid crystal device and more particularly relates to a liquid crystal device which is suited for manufacturing a thermal writing type liquid crystal device having a prolonged service life.
Liquid crystal devices wherein a thermo-optic effect of a liquid crystal having a smectic phase is utilized, which are examples of thermal writing type liquid crystal devices, are described in detail in, for example, S. Lu et al. "Thermally-Addressed Pleochroic Dye Switching Liquid Crystal Display" (SID 82 DIGEST, pp. 238-239 (1982)), a paper by S. LeBerre et al. "A Flat Smectic Liquid Crystal Display" (SID 82 DIGEST, pp. 252-253), and U.S. patent application Ser. No. 521,900, now U.S. Pat. No. 4,548,474, issued Oct. 22, 1985.
FIG. 1 shows the basic structure of the liquid crystal device described in the above-cited paper. A liquid crystal 1 having a smectic phase is sandwiched between two glass substrates 2 and 3. The lower glass substrate 3 which serves as a support for both the liquid crystal and an electrode for generating heat is provided with a heat electrode 4 which is an electrode for generating heat. The upper substrate 2 is provided with a transparent electrode 5, and these two electrodes form an X-Y matrix structure.
Information can be written in a liquid crystal by energizing any heat electrode, heating the liquid crystal with generated Joule's heat, thereby allowing the liquid crystal to transfer into an isotropic phase or a nematic phase, and changing the state of orientation of the liquid crystal according to the presence or absence of an electric field applied to the liquid crystal during the course of its cooling.
Nevertheless, the temperature of the heat electrode itself is known to increase to about 100.degree. to 150.degree. C. to attain writing. Therefore, thermal expansion of the heat electrode itself must not be neglected.
In conventional liquid crystal device structures, the heat electrode has been formed by vacuum-depositing a metal such as Al directly on a glass substrate and etching the deposited film. Therefore, when the electrode is heated, a thermal stress is produced between the heat electrode and the glass substrate due to the difference between their coefficients of thermal expansion, so that the heat electrode fails or peels from the glass base, resulting in a decrease in the service life of the liquid crystal device.